APPLICANT'S ABSTRACT: A 4-year continuation and expansion of our existing study of the pulmonary effects of habitual use of marijuana is proposed to investigate the following: 1) the role of marijuana in respiratory tract carcinogenesis; 2) the effect of habitual marijuana smoking on pulmonary host defenses; and 3) mechanisms that might account for our observations of the association of marijuana with lung inflammation. Over a 4-year period, 32 smokers in each of the following smoking categories, marijuana only [MS], tobacco only [TS], marijuana plus tobacco [MTS] and nonsmokers [NS], will undergo fiberoptic bronchoscopy (using a new fluorescence endoscopic system which is sensitive in detecting severe bronchial dysplasia), auto-fluorescence-guided bronchial mucosal biopsies, bronchial washings, and bronchoalveolar lavage (BAL). Bronchial epithelial cells and tissue (obtained by fluorescence bronchoscopy), BAL fluid and alveolar macrophages (AMs) isolated therefrom will be used to accomplish the following specific objectives: 1) to assess the relative risk of smoking marijuana and tobacco, alone and in combination, for the development of moderate to severe dysplasia (a serious precursor lesion to bronchogenic carcinoma); 2) to determine whether marijuana smoking, on a per cigarette basis, activates the P4501A1 enzyme pathway (which converts polycyclic aromatic hydrocarbons present in the tar fraction of tobacco and marijuana smoke into active carcinogens) to a greater degree than tobacco smoking; 3) to extend the previous descriptive histopathological observations of bronchial epithelial changes in marijuana smokers in a mechanistic and molecular direction by studying specific genes and gene products thought relevant to human lung cancer progression; 4) to evaluate the effects of marijuana and tobacco smoking, singly and in combination, on the uptake, killing and destruction of bacteria by AMs, as well as the mechanisms associated with these anti- bacterial effects; 5) to determine the role of inflammatory cytokines, including macrophage-colony stimulating factor (M-CSF), interleukin-8 (lL-8), tumor necrosis factor-alpha (TNF-alpha) and transforming growth factor-Beta 1, (TGF-Beta 1), as specific mediators of inflammation induced by smoking marijuana and/or tobacco; and 6) to determine whether the increased numbers of neutrophils which we have previously found in BAL fluid from smokers of marijuana and/or tobacco are activated, as reflected by their release into BAL fluid of increasing amounts of defensins and proteases that convert alpha 2-macroglobulin to its fast electrophoretic form.